Mould on Walls in Singapore: Why It Happens and How to Fix It

Tintin Painting · Painting Tips · 6 min read

Singapore sits at 80%+ relative humidity most of the year. That's excellent for plants and terrible for walls. Mould on interior walls is one of the most common things we're called about, and it's also the thing most commonly handled badly.

Why Walls Grow Mould Here

Mould needs three things: moisture, a food source, and still air. Singapore homes supply all three readily.

• Condensation. Air-conditioned rooms against humid outside air produce condensation on the cooler surface. That's why mould so often appears on external-facing walls and around aircon units.
• Poor ventilation. Bathrooms without working extractor fans, wardrobes pushed flush against walls, and rooms kept closed up all trap moist air against a surface.
• Water ingress. Leaking pipes, failed bathroom waterproofing, or seepage from a neighbouring unit. This is the serious category.

The Mistake Almost Everyone Makes

Painting over it. Including painting over it with anti-mould paint.

Mould has root structures that penetrate below the paint surface. Coating over live mould traps it, feeds it the moisture already in the wall, and it grows back through the new paint — usually within two to six months, often looking worse than before. Anti-mould paint is a preventive product for a clean, dry, treated surface. It is not a treatment for existing growth.

If a contractor offers to "just paint over" visible mould, that's a genuine red flag about the rest of their work.

What Proper Treatment Actually Involves

1. Find the moisture source first. This is the step that gets skipped. If there's an active leak or failed waterproofing, no amount of surface treatment will hold. Sometimes this means the real fix is a plumber or a waterproofing contractor, not a painter — and we'll tell you that rather than take the job.
2. Remove affected material. Surface growth can be treated in place. Where mould has gone into the plaster, that section has to come out. Painting over compromised plaster just delays the problem.
3. Treat and kill the growth. A proper fungicidal wash, applied and left to work, not wiped straight off.
4. Let it dry completely. This is why mould treatment adds a day to a job. Sealing moisture into a wall recreates the exact conditions that caused the problem.
5. Seal, then prime. A stain-blocking sealer stops residual discolouration bleeding through the new coats.
6. Then paint, ideally with an anti-mould or moisture-resistant product in the affected room.

Where It Shows Up Most

In our experience across Singapore flats: bathroom ceilings and the wall above the shower; behind and beside wardrobes on external walls; around and below aircon units; kitchen walls near the sink; and window reveals in bedrooms that are kept closed and air-conditioned.

Coastal-adjacent estates — Bedok, Pasir Ris, East Coast — see it slightly more often, as do older blocks where the original waterproofing has aged.

Keeping It From Coming Back

• Run bathroom extractor fans during and for 15–20 minutes after showering. If yours doesn't work, fixing it is cheaper than repainting.
• Leave a few centimetres of gap between large furniture and external walls so air can move.
• Open windows for a while daily, even briefly, in rooms that are usually air-conditioned.
• Deal with small leaks immediately rather than watching them.
• Use moisture-resistant products in bathrooms and kitchens rather than standard emulsion.

When It's Not a Painting Job

Be honest with yourself about scale. Widespread mould across multiple rooms, growth that returns within weeks of treatment, or visible damp patches that spread usually point to a structural moisture problem — failed waterproofing, a hidden leak, or seepage from the unit above. That needs diagnosing and fixing before any painter can help you.

If you're in an HDB flat and suspect seepage from the unit above, HDB has a Goodwill Repair Assistance scheme worth looking into, and the issue is between the two households rather than something a repaint resolves.

We'd rather tell you that upfront than take your money for a paint job that fails.

Common Questions